1. Field of the Invention
The present invention relates to an organic photosensitive member for use in electrophotographic instruments such as copying machines and various printers.
2. Description of the Prior Art
In recent years, electrophotographic technologies have been widely used not only in the field of copying machines, but also in the field of various printers, because of their instantaneity and high image quality.
Photosensitive members for electrophotography (may hereinafter referred to as "photosensitive members"), which are the core of electrophotographic technologies, have so far been typified by inorganic photosensitive members using inorganic materials such as selenium, arsenic-selenium alloys, cadmium sulfide, and zinc oxide. Recently, organic photosensitive members using organic materials, which are pollution-free and advantageous in terms of facilitated film formation and production, flexibility, light weight, and usability of wide varieties, have been developed and put to practical use.
Organic photosensitive members include so-called laminate type photosensitive members having a photosensitive layer comprising a laminate of a charge generating layer and a charge transporting layer. The laminate type photosensitive members have many advantages such that highly efficient charge generating substances and charge transporting substances may be selected and combined so as to impart high sensitivity, that wide varieties of highly safe materials can be selected, and that film formation can be performed by coating, thus leading to high productivity at lower prices. Since the laminate type photosensitive members are highly likely to become predominant photosensitive members, they are under eager research and development.
A photosensitive member is usually constructed by providing a photosensitive layer on an electroconductive substrate made of aluminum or the like. The surface condition of the substrate greatly affects the characteristics of the photosensitive member. Dirt, foreign matter or scar on the surface of the substrate affects electrophotographic characteristics, possibly causing an image defect. To eliminate such a defect on the substrate surface, surface roughening or mirror finishing is applied to the surface. In many cases, however, the aluminum for use as the substrate is an aluminum alloy containing Mg or Mn. No matter what precision finishing the substrate is subjected to, its surface involves a defect such as a burr or tipping due to the crystallization of the metal incorporated. In addition, aluminum is a chemically active element, so that the surface of the substrate finished tends to be oxidized. Since the oxidation does not proceed uniformly, the resulting oxide film has irregularities, and the substrate surface differs in activity from portion to portion. If a photosensitive layer is provided on such substrate surface, the photosensitive layer has uneven thicknesses, and a layer defect such as a void or crater may easily occur, thus degrading the quality of the resulting image. As a measure for eliminating such influences of the substrate surface, it has been practiced to provide an undercoating layer on the substrate surface. Known examples of the undercoating layer include an inorganic layer of an aluminum anode oxide film, aluminum oxide or aluminum hydroxide, and an organic layer of polyvinyl alcohol, casein, polyvinyl pyrrolidone, polyacrylic acid, cellulose, gelatin, starch, polyurethane, polyimide, or polyamide.
It is well known to use an alcohol-soluble polyamide for an undercoating layer. For example, Japanese Patent Application Publication No. 4382/1973, Japanese Patent Application Publication No. 45707/1983, and Japanese Patent Application Laying-Open No. 168157/1985 disclose the formation of an undercoating layer from an alcohol-soluble polyamide resin. Japanese Patent Application Laying-Open No. 101853/1988 discloses an undercoating layer consisting essentially of an alcohol-soluble polyamide and further containing a water-soluble polyamide.
A first property required of the undercoating layer is to exert no adverse influence on electrophotographic characteristics. To fulfill this requirement, the undercoating layer must have low electric resistance, and the electric resistance must not vary according to the change of the environment. A second requirement is the lack of the function to inject carriers into the charge generating layer. An undercoating layer having the function to inject carriers into the charge generating layer decreases charge potential, thereby causing a decrease in image contrast and inducing a fog. A third requirement is that the undercoating layer can be as thick as possible in order to cover up various defects on the substrate surface. Moreover, the thick layer must keep a good adhesion to the substrate surface. As a fourth requirement, when the undercoating layer is to be formed by a coating process, the coating fluid must be stable.
The undercoating layers so far known have not been entirely satisfactory in fulfilling the above requirements. The use of the aforementioned alcohol-soluble polyamide as the undercoating layer, for instance, has been defective in that it adversely affects the electrophotographic characteristics. The use of an azo pigment as a charge generating substance in the charge generating layer, in particular, has exerted markedly adverse influences on properties such as photosensitivity and residual potential, and has deteriorated image quality.